This invention relates to vitamin D compounds, and more particularly to vitamin D derivatives substituted at the carbon 2 position.
The natural hormone, 1xcex1,25-dihydroxyvitamin D3 and its analog in ergosterol series, i.e. 1xcex1,25-dihydroxyvitamin D2 are known to be highly potent regulators of calcium homeostasis in animals and humans, and more recently their activity in cellular differentiation has been established, Ostrem et al., Proc. Natl. Acad. Sci. U.S.A., 84 2610 (1987). Many structural analogs of these metabolites have been prepared and tested, including 1xcex1-hydroxyvitamin D3, 1xcex1-hydroxyvitamin D2, various side chain homologated vitamins and fluorinated analogs. Some of these compounds exhibit an interesting separation of activities in cell differentiation and calcium regulation. This difference in activity may be useful in the treatment of a variety of diseases.
Recently, a new class of vitamin D analogs has been discovered, i.e. the so called 19-nor-vitamin D compounds, which are characterized by the replacement of the A-ring exocyclic methylene group (carbon 19), typical of the vitamin D system, by two hydrogen atoms. Biological testing of such 19-nor-analogs (e.g., 1xcex1,25-dihydroxy-19-nor-vitamin D3) revealed a selective activity profile with high potency in inducing cellular differentiation, and very low calcium mobilizing activity. Thus, these compounds are potentially useful as therapeutic agents for the treatment of malignancies, or the treatment of various skin disorders. Two different methods of synthesis of such 19-nor-vitamin D analogs have been described (Perlman et al., Tetrahedron Lett. 31 1823 (1990); Perlman et al., Tetrahedron Lett. 32, 7663 (1991), and DeLuca et al., U.S. Pat. No. 5,086,191).
In U.S. Pat. No. 4,666,634, 2xcex2-hydroxy and alkoxy (e.g., ED-71) analogs of 1xcex1,25-dihydroxyvitamin D3 have been described and examined by Chugai group as potential drugs for osteoporosis and as antitumor agents. See also Okano et al., Biochem. Biophys. Res. Commun. 163, 1444 (1989). Other 2-substituted (with hydroxyalkyl, e.g., ED-120, and fluoroalkyl groups) A-ring analogs of 1xcex1,25-dihydroxyvitamin D3 have also been prepared and tested (Miyamoto et al., Chem. Pharm. Bull. 41, 1111 (1993); Nishii et al., Osteoporosis Int. Suppl. 1, 190 (1993); Posner et al., J. Org. Chem. 59, 7855 (1994), and J. Org. Chem. 60, 4617 (1995)).
Recently, 2-substituted analogs of 1xcex1,25-dihydroxy-19-nor-vitamin D3 have also been synthesized, i.e. compounds substituted at 2-position with hydroxy or alkoxy groups (DeLuca et al., U.S. Pat. No. 5,536,713), which exhibit interesting and selective activity profiles. All these studies indicate that binding sites in vitamin D receptors can accommodate different substituents at C-2 in the synthesized vitamin D analogs.
The discovery of the hormonally active form of vitamin D3, 1xcex1,25-dihydroxyvitamin D3 (1xcex1,25xe2x80x94(OH)2D3, calcitriol, 1; FIG. 1), has greatly stimulated research into its physiology and chemistry. As previously noted, it has been established that 1 not only regulates the mineral metabolism in animals and humans, but also exerts potent effects upon cell proliferation and cellular differentiation. Therefore, the chemistry of vitamin D has been recently focused on the design and synthesis of analogs that can exert selective biological actions.
In a previous investigation of the structure-activity relationship of the vitamin D molecule, an analog of the natural hormone 1, 1xcex1,25-dihydroxy-2-methylene-19-nor-vitamin D3 (2), was prepared in which the exocyclic methylene group is transposed, in comparison with 1, from C-10 to C-2. Also, 2xcex1-methyl analog 3 was obtained by selective hydrogenation of 2. Both analogs were characterized by significant biological potency, enhanced especially in their isomers in the 20S-series.
In a continuing search for biologically active vitamin D compounds novel 19-nor analogs of 1, substituted at C-2 with ethylidene (4a,b and 5a,b) and ethyl (6a,b and 7a,b) groups, have now been synthesized and tested. Structurally the novel 2-ethylidene analogs belong to a class of 19-nor vitamin D compounds characterized by the general formula I shown below: 
where Y1 and Y2, which may be the same or different, are each selected from the group consisting of hydrogen and a hydroxy-protecting group, and where the group R represents any of the typical side chains known for vitamin D type compounds.
Structurally the novel 2-ethyl analogs belong to a class of 19-nor vitamin D compounds characterized by the general formula II shown below: 
where Y1 and Y2, which may be the same or different, are each selected from the group consisting of hydrogen and a hydroxy-protecting group, and where the group R represents any of the typical side chains known for vitamin D type compounds.
More specifically R can represent a saturated or unsaturated hydrocarbon radical of 1 to 35 carbons, that may be straight-chain, branched or cyclic and that may contain one or more additional substituents, such as hydroxy- or protected-hydroxy groups, fluoro, carbonyl, ester, epoxy, amino or other heteroatomic groups. Preferred side chains of this type are represented by the structure below: 
where the stereochemical center (corresponding to C-20 in steroid numbering) may have the R or S configuration, (i.e. either the natural configuration about carbon 20 or the 20-epi configuration), and where Z is selected from Y, xe2x80x94OY, xe2x80x94CH2OY, xe2x80x94Cxe2x89xa1CY, xe2x80x94CHxe2x95x90CHY, and xe2x80x94CH2CH2CHxe2x95x90CR3R4, where the double bond may have the cis or trans geometry, and where Y is selected from hydrogen, methyl, xe2x80x94COR5 and a radical of the structure: 
where m and n, independently, represent the integers from 0 to 5, where R1 is selected from hydrogen, deuterium, hydroxy, protected hydroxy, fluoro, trifluoromethyl, and C1-5-alkyl, which may be straight chain or branched and, optionally, bear a hydroxy or protected-hydroxy substituent, and where each of R2, R3, and R4, independently, is selected from deuterium, deuteroalkyl, hydrogen, fluoro, trifluoromethyl and C1-5 alkyl, which may be straight-chain or branched, and optionally, bear a hydroxy or protected-hydroxy substituent, and where R1 and R2, taken together, represent an oxo group, or an alkylidene group, xe2x95x90CR2R3, or the group xe2x80x94(CH2)pxe2x80x94, where p is an integer from 2 to 5, and where R3 and R4, taken together, represent an oxo group, or the group xe2x80x94(CH2)qxe2x80x94, where q is an integer from 2 to 5, and where R5 represents hydrogen, hydroxy, protected hydroxy, C1-5 alkyl or xe2x80x94OR7 where R7 represents C1-5 alkyl, and wherein any of the CHxe2x80x94 groups at positions 20, 22, or 23 in the side chain may be replaced by a nitrogen atom, or where any of the groups xe2x80x94CH(CH3)xe2x80x94, xe2x80x94CH(R3)xe2x80x94, or xe2x80x94CH(R2)xe2x80x94 at positions 20, 22, and 23, respectively, may be replaced by an oxygen or sulfur atom.
The wavy lines, e.g. to the substituents at C-2 and at C-20 indicate that those substituents may have either the R or S configuration.
Specific important examples of side chains with natural 20R-configuration are the structures represented by formulas (a), b), (c), (d) and (e) below. i.e. the side chain as it occurs in 25-hydroxyvitamin D3 (a); vitamin D3 (b); 25-hydroxyvitamin D2 (c); vitamin D2 (d); and the C-24 epimer of 25-hydroxyvitamin D2 (e): 
Specific important examples of side chains with the unnatural 20S (also referred to as the 20-epi) configuration are the structures presented by formulas (f), (g), (h), (i) and (j) below: 
The above novel compounds exhibit a desired, and highly advantageous, pattern of biological activity. The synthesized vitamins were tested for their ability to bind the porcine intestinal vitamin D receptor. The presented results (FIG. 5) indicate that 2-ethylidene-19-norvitamins, possessing methyl group from ethylidene moiety directed toward C-3, i.e., trans in relation to C(6)xe2x80x94C(7) bond (isomers E), are more active than 1xcex1,25xe2x80x94(OH)2D3 in binding to VDR, whereas their counterparts with cis relationship between ethylidene methyl substituent and C(7)xe2x80x94H group (isomers Z) exhibit significantly reduced affinity for the receptor. The competitive binding analysis showed also that 2xcex1-ethyl-19-norvitamins bind to the receptor better than their isomers with 2xcex2-ethyl substituents (FIG. 6). In the next assay, the cellular activity of the synthesized compounds was established by studying their ability to induce differentiation of human promyelocyte HL-60 cells into monocytes. E isomer of (20S)-2-ethylidene-19-nor-vitamin D3 (FIG. 7) and both 2xcex1-ethyl-19-norvitamins (FIG. 8) are more potent than 1xcex1,25xe2x80x94(OH)2D3 in this assay, whereas the remaining tested compounds are almost equivalent to the hormone 1. Both E isomers of 2-ethylidene-19-norvitamins, when tested in vivo in rats (Table 1) exhibited very high calcemic activity, the (20S)-compound being especially potent. On the contrary, isomeric Z compounds are significantly less active. 2-Ethyl-19-norvitamins have some ability to mobilize calcium from bone but not to the extent of the hormone 1, while being inactive in intestine. The only exception is the 2xcex1-ethyl isomer from the 20S-series which shows strong calcium mobilization response and marked intestinal activity.
These compounds are thus highly specific in their calcemic activity. Their preferential activity on mobilizing calcium from bone and either high or normal intestinal calcium transport activity allows the in vivo administration of these compounds for the treatment of metabolic bone diseases where bone loss is a major concern. Because of their preferential calcemic activity on bone, these compounds would be preferred therapeutic agents for the treatment of diseases where bone formation is desired, such as osteoporosis, especially low bone turnover osteoporosis, steroid induced osteoporosis, senile osteoporosis or postmenopausal osteoporosis, as well as osteomalacia and renal osteodystrophy. The treatment may be transdermal, oral or parenteral. The compounds may be present in a composition in an amount from about 0.1 xcexcg/gm to about 50 xcexcg/gm of the composition, and may be administered in dosages of from about 0.01 xcexcg/day to about 50 xcexcg/day.
The compounds of the invention are also especially suited for treatment and prophylaxis of human disorders which are characterized by an imbalance in the immune system, e.g. in autoimmune diseases, including multiple sclerosis, diabetes mellitus, host versus graft reaction, lupus, atherosclerosis, and rejection of transplants; and additionally for the treatment of inflammatory diseases, such as inflammatory bowel disease, rheumatoid arthritis and asthma, as well as the improvement of bone fracture healing and improved bone grafts. Acne, alopecia especially chemically induced alopecia (e.g. resulting from chemotherapy), skin conditions such as dermatitis, eczema, keratosis, dry skin (lack of dermal hydration), undue skin slackness (insufficient skin firmness), insufficient sebum secretion and wrinkles, as well as hypocalcemia, hypoparathyroidism and hypertension are other conditions which may be treated with the compounds of the invention.
The above compounds are also characterized by high cell differentiation activity. Thus, these compounds also provide therapeutic agents for the treatment of psoriasis, or as an anti-cancer agent, especially against leukemia, colon cancer, breast cancer and prostate cancer. The compounds may be present in a composition to treat psoriasis, cancer, and/or the above list of diseases in an amount from about 0.01 xcexcg/gm to about 100 xcexcg/gm of the composition, and may be administered topically, transdermally, orally or parenterally in dosages of from about 0.01 xcexcg/day to about 100 xcexcg/day.
This invention also provides novel intermediate compounds formed during the synthesis of the end products.
This invention also provides a novel synthesis for the production of the end products of structures I and II. Two different synthetic paths were devised, both based on Lythgoe type Wittig-Homer coupling of the A-ring fragments, the corresponding phosphine oxides prepared from quinic acid, with the protected 25-hydroxy Grundmann""s ketone. In the first method, the allylic phosphine oxides were substituted at C-4xe2x80x2 with the ethylidene group whereas in the alternative approach the introduction of ethylidene moiety was performed in the final step of the synthesis, by Wittig reaction of the intermediate 2-oxo-vitamin D analog. The selective catalytic hydrogenation of 2-ethylidene analogs of 1xcex1,25-dihydroxy-19-norvitamin D3 provided the corresponding 2xcex1- and 2xcex2-ethyl compounds.